An engine of a vehicle is usually started by operation of an ignition switch. The ignition switch is operated by an ignition key inserted into a key slot and then turned to a predetermined position. The ignition switch has an off (OFF) position for insertion and removal of the ignition key, an accessory (ACC) position for energizing electrical accessories, for example, car audio system and the like, an on (IG-ON) position for energizing an ignition system of the engine, and an engine start (ST) position for energizing a starter thereby starting the engine. The ignition key in the engine start position returns to the on position unless a driver applies force to the key to hold the key in the engine start position. The ignition key in any of other positions stays at the original position even if the driver releases the key.
Recently, control of the start of the engine as mentioned above has been exercised by a computer which generally controls a start system. Japanese Patent Publication No. 7-6469 (Japanese Patent Laying-Open No. 63-297767, corresponding to U.S. Pat. No. 4,862,010) discloses an engine start method by means of a computer.
The disclosed engine start method includes the steps of: starting a current supply to an exciting coil of an electromagnet switch upon receiving an engine start instruction signal from an ignition switch and continuously closing the electromagnet switch; checking various conditions to detect whether or not there is a trouble with initiation of the start of the engine after the current supply to the exciting coil of the electromagnet switch is started and before the electromagnet switch is closed; stopping the current supply to the exciting coil of the electromagnet switch if there is a trouble; starting the engine by a current supply to a starter upon the closure of the electromagnet switch; checking various conditions to detect whether or not there is a trouble with continuation of the start of the engine after the electromagnet switch is closed and before the start of the engine is completed; stopping the current supply to the exciting coil of the electromagnet switch if there is a trouble; and stopping the current supply to the exciting coil of the electromagnet switch when it is determined that the start of the engine is completed.
According to the disclosed engine start method, in starting the engine, namely in the period from the start of the current supply to the electromagnet switch to the start of the engine, various conditions are checked by the computer to detect whether or not there is a trouble with the initiation of the start of the engine and the continuation of the start. If any trouble is found by the check, the supply of the exciting current is stopped until the start of the engine is completed. The process is thus efficient and, for example, it is possible to prevent an automobile from suddenly moving forward when the shift lever is operated in a cranking process and thereby achieve a safe automatic start.
However, the disclosed engine start method as described above has the following problems. The starter for starting the engine of the vehicle is supplied with electric power from a battery installed in the vehicle. The starter cranks the engine which has been stopped so as to start the engine. Therefore, the starter requires a large starting current. Then, as a computer is supplied with electric power from the same battery installed in the vehicle, a supply voltage from the vehicle-installed-battery to the computer could be lower than an operating voltage of the computer when the starter is rotating. In this situation, the above-described engine start method cannot be used to start the engine. In order to avoid such a situation, the voltage which ensures the operation of the computer may be lowered. This approach, however, requires a considerably high reliability of the computer, resulting in a cost increase.
It is thus an object of the present invention to provide an engine start control device and a control method by which an engine can be started even if a computer of an engine start system is inoperative.
It is another object of the present invention to provide an engine start control device and a control method of low cost by which an engine can be started even if a computer of an engine start system is inoperative.